LED lighting technology is rapidly developing to replace traditional incandescent and fluorescent lightings. LED tube lamps are mercury-free in comparison with fluorescent tube lamps that need to be filled with inert gas and mercury. Thus, it is not surprising that LED tube lamps are becoming a highly desired illumination option among different available lighting systems used in homes and workplaces, which used to be dominated by traditional lighting options such as compact fluorescent light bulbs (CFLs) and fluorescent tube lamps. Benefits of LED tube lamps include improved durability and longevity and far less energy consumption; therefore, when taking into account all factors, they would typically be considered as a cost effective lighting option.
Typical LED tube lamps have a lamp tube, a circuit board disposed inside the lamp tube with light sources being mounted on the circuit board, and end caps accompanying a power supply provided at two ends of the lamp tube with the electricity from the power supply transmitting to the light sources through the circuit board. However, existing LED tube lamps have certain drawbacks.
Grainy visual appearances are also often found in the aforementioned conventional LED tube lamp. The LED chips spatially arranged on the circuit board inside the lamp tube are considered as spot light sources, and the lights emitted from these LED chips generally do not contribute uniform illuminance for the LED tube lamp without proper optical manipulation. As a result, the entire tube lamp would exhibit a grainy or non-uniform illumination effect to a viewer of the LED tube lamp, thereby negatively affecting the visual comfort and even narrowing the viewing angles of the lights. As a result, the quality and aesthetics requirements of average consumers would not be satisfied. To address this issue, the Chinese patent application with application no. CN 201320748271.6 discloses a diffusion tube is disposed inside a glass lamp tube to avoid grainy visual effects.
However, the disposition of the diffusion tube incurs an interface on the light transmission path to increase the likelihood of total reflection and therefore decrease the light outputting efficiency. In addition, the optical rotatory absorption of the diffusion tube decreases the light outputting efficiency.
Furthermore, all of the electronic components of the power supply circuit disclosed in the Chinese patent application with application no. CN 201320748271.6 are in the end caps. The heat dissipation of the power supply circuit in the small space of the end cap illustrated in the Chinese application is insufficient, therefore the power supply circuit is easier to be damaged.
Next, the driving of an LED uses a DC driving signal. The driving signal for a fluorescent lamp is a low-frequency and low-voltage AC signal as provided by an AC powerline, a high-frequency and high-voltage AC signal provided by a ballast, or even a DC signal provided by a battery for emergency lighting applications. Since the voltages and frequency spectrums of these types of signals differ significantly, simply performing a rectification to produce the required DC driving signal in an LED tube lamp is not competent at achieving the LED tube lamp's compatibility with traditional driving systems of a fluorescent lamp.
Common main types of ballast include instant-start ballast and program-start ballast. A ballast typically includes a resonant circuit and is designed to match the loading characteristics of a fluorescent lamp in driving the fluorescent lamp. However, an LED is a nonlinear component with significantly different characteristics from a fluorescent lamp. Therefore, using an LED tube lamp with an electrical ballast impacts the resonant circuit design of the electrical ballast, causing a compatibility problem. Generally, a program-start ballast will detect the presence of a filament in a fluorescent lamp, but traditional LED driving circuits cannot support the detection and may cause a failure of the filament detection and thus failure of the starting of the LED tube lamp. Further, electrical ballast is in effect a current source, and when it acts as a power supply of a DC-to-DC converter circuit in an LED tube lamp, problems of overvoltage and overcurrent or undervoltage and undercurrent are likely to occur, resulting in damaging of electronic components in the LED tube lamp or unstable provision of lighting by the LED tube lamp.
Accordingly, the prevent disclosure and its embodiments are herein provided.